Introductory and Historical 



'I have suggested that senescence is the result of the con- 

 tinued action of the regulator after growth is stopped. The 

 regulator does efficiently all that concerns the welfare of the 

 species. Man is within 2 cm. of the same height between 18 

 and 60, he gently rises 2 cm. between 20 and 27, and still more 

 gently loses 1 cm. by 40 or thereabouts. If primitive man at 

 18 begat a son, the species had no more need of him by 37, 

 when his son could hunt for food for the grandchildren. There- 

 fore the dwindling of cartilage, muscle and nerve cell, which 

 we call senescence, did not affect the survival of the species, the 

 checking of growth had secured that by ensuring a perfect 

 physique between 20 and 40. Effects of continued negative 

 growth after 37 were of indifference to the race; probably no 

 man ever reached 60 years old until language attained such 

 importance in the equipment of the species that long experi- 

 ence became valuable in a man who could neither fight nor 

 hunt. This negative growth is not the manifestation of a weak- 

 ness inherent in protoplasm or characteristic of nucleated cells; 

 it is the unimportant by-product of a regulating mechanism 

 necessary to the survival of swiftly moving land animals, a 

 mechanism evolved by selection and survival as have been 

 evolved the jointing of mammalian limbs, and with similar 

 perfection' (Bidder, 1932). 



Bidder's theory, besides raising the question of senescence as 

 an effect lying outside the 'programme' imposed by natural 

 selection, poses the highly important suggestion that there may 

 be two categories of vertebrates — those whose life span is fixed 

 as in mammals, and those whose life-span is not fixed. From 

 the theoretical point of view the establishment of the truth or 

 falsity of this suggestion might be the key problem in the elucid- 

 ation of mammalian ageing, since the disproof of almost all the 

 major existing theories of senescence would follow from the 

 demonstration that it is not universally present in vertebrates. 

 This might appear a simple issue of fact, but for reasons which 

 will appear later, no such demonstration one way or the other 

 has yet been forthcoming. 



Bidder's theory marks the last major attempt to produce a 

 hypothesis of vertebrate senescence. No significant theory of 



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